The pleiotropic cytokine tumor necrosis factor alpha (TNFα) is associated with inflammation and binds to cells through membrane receptor molecules, including two molecules having molecular weights of approximately 55 kDa and 75 kDa (p55 and p75). In addition to binding TNFα, the p55 and p75 TNF receptors mediate the binding to cells of homotrimers of TNFβ, which is another cytokine associated with inflammation and which shares structural similarities with TNFα (e.g., see Cosman, Blood Cell Biochem 7:51-77, 1996). TNFβ is also known as lymphotoxin-α (LTα).
It has been proposed that a systemic or localized excess of TNFα contributes to the progression of numerous medical disorders. For example, patients with chronic heart failure have elevated levels of serum TNFα, which have been shown to increase with disease progression (see, for example, Levine et al., N Eng J Med 323:236-241, 1990). A variety of other diseases are associated with elevated levels of TNFα (see, for example, Feldman et al., Transplantation Proceedings 30:4126-4127, 1998).
Psoriatic arthritis (PsA) is a chronic autoimmune condition that shares some features with both rheumatoid arthritis (RA) and the inflammatory skin disease psoriasis (for review, see Breathnach, In Klippel and Dieppe eds. Rheumatology, 2nd Ed., Mosby, 1998, 22.1-22.4). Psoriasis is characterized by epidermal keratinocyte hyperproliferation, accompanied by neutrophil and T cell infiltration, and is associated with elevated levels of inflammatory cytokines, including TNFα, IL-6 and TGFβ (see, for example, Bonifati et al., Clin Exp Dermatol 19:383-387, 1994). Psoriasis and PsA are different clinical entities, and are associated with somewhat different MHC haplotypes (Gladman, Rheum Dis Clin NA. 18:247-256, 1992; Breathnach, 1998). The overall prognosis for PsA is far worse than for ordinary psoriasis. Nonetheless, treatments used for the psoriatic lesions of PsA generally are similar to those used to treat psoriasis.
Psoriatic skin lesions are present in patients with PsA, although only a minority of psoriasis sufferers actually have PsA. Ordinary psoriasis occasionally is accompanied by joint pain, but does not involve the extreme pain and often deforming degeneration of joints and bone that occurs in PsA patients.
Treatments that sometimes are effective in treating ordinary psoriasis include topical medications (e.g., steroids, coal tar, anthralin, Dead Sea salts, various natural oils, vitamin D3 and its analogs, sunshine, topical retinoids), phototherapy (e.g., ultraviolet light, photochemotherapy (PUVA)), and internal medications (e.g., methotrexate, systemic steroids, oral retinoids, cyclosporine, or a rotating regimen of these three). In addition, it has been proposed that psoriasis could be treated with TNF-derived peptides, quinolinesulfonamides, pyrrolidinone derivatives, catechol diether compounds, isoxazoline compounds, matrix metalloproteinase inhibitors or mercapto alkyl peptidyl compounds, all of which inhibit either TNFα production or its release from cultured cells (see, for example, U.S. Pat. No. 5,691,382, U.S. Pat. No. 5,834,485, U.S. Pat. No. 5,420,154, U.S. Pat. No. 5,563,143, U.S. Pat. No. 5,869,511 and U.S. Pat. No. 5,872,146), as well as with various combination therapies involving TNFα antagonists (for example, see U.S. Pat. No. 5,888,511 or U.S. Pat. No. 5,958,413).
Conflicting results have been reported regarding the role of TNFα in psoriasis. Some investigators have proposed that overproduction of TNFα contributes to the pathology of psoriasis (e.g., Pigatto et al., J Invest Dermatol 94:372-376, 1990; Sagawa et al., Dermatol 187:81-83, 1993; Ameglio et al., Dermatol 189:359-363, 1994). One group reported some improvement after treatment with pentoxifylline, a drug that can inhibit the release of TNFα, but which exerts many of its physiological effects by inhibiting cyclic AMP phosphodiesterase (Omulecki et al., J Am Acad Dermatol 34:714-715, 1996; Centola et al., J Androl 16:136-142, 1995; Elferinck et al., Biochem Pharmacol 54:475-480, 1997). However, other reports have cast doubt on the hypothesis that overproduction of TNFα exacerbates psoriasis. For example, some investigators have reported that treatment with TNFα itself actually can mitigate psoriasis (see, e.g., Takematsu et al., Br J Dermatol 124:209-210, 1991; Creaven et al., J Am Acad Dermatol 24:735-737, 1991).
In addition to psoriatic lesions, PsA is characterized by distal interphalangeal joint (DIP) involvement, enthesopathy, nail lesions, spondylitis and dactylitis. The histopathogenesis of PsA and the more well-studied rheumatoid arthritis share certain features. In both RA and in active PsA, patients exhibit increased levels of HLA-DR+ T cells and MHC class II antigens in their synovial membranes and synovial fluid, as well as increased expression of the cytokine TNFα. In addition, both diseases are associated with prominent synovial vascular changes.
The discovery of rheumatoid factor in the serum of RA patients provided an important tool for differentiating PsA from RA, but the realization that RA and PsA are distinct diseases was based primarily on their many clinical differences (e.g., Helliwell and Wright, In Klippel and Dieppe eds. Rheumatology, 2nd Ed., Mosby, 1998, 21.1-21.8). Studies have shown that levels of TNFα, Il-1β, Il-8 as well as TNFα receptors in synovial fluids were higher in PsA patients than in osteoarthritis patients, though they were lower than in RA patients (Partsch et al., J Rheumatol 24:518-523, 1997; Partsch et al., J Rheumatol 25:105-110, 1998; Partsch et al., Ann Rheum Dis 57:691-693, 1998). PsA is distinguished from RA also by radiographic appearance, a notably higher degree of synovial membrane vascularity as well as differences in the levels of various cytokines in the synovial fluids (Ritchlin et al., J Rheumatol 25:1544-52, 1998; Veale et al., Arth Rheum 36:893-900, 1993). Veale et al. noted differences in synovial membrane adhesion molecules and numbers of macrophages when they compared RA and PsA patients, as well as observing a minimal degree of hyperplasia and hypertrophy of synoviocytes in PsA as compared with RA patients. Because of such differences, coupled with the association of PsA but not RA with class I MHC antigens, Ritchlin et al. have suggested that PsA must be triggered by different mechanisms than those underlying RA. Veale et al. suggested for similar reasons that different cytokines were likely to be interacting in the synovium of PsA and RA patients.
Most of the drugs used for treating the arthritic aspects of PsA are similar to those used in RA (Salvarini et al., Curr Opin Rheumatol 10:229-305, 1998), for example the non-steroidal antiinflammatories (NSAIDs), which may be used alone or in combination with the disease-modifying anti-rheumatic drugs, or “DMARDs.” However, one group found that long-term administration of the DMARD methotrexate failed to slow the progression of joint damage in PsA patients (Abu-Shakra et al., J Rheumatol 22:241-45, 1995), and another group reported very little improvement in PsA patients who had received methotrexate (Willkens et al., Arthr Rheum 27:376-381, 1984). Similarly, Clegg et al. found only a slight improvement over placebo in PsA patients treated with sulfasalazine, another drug classified as a DMARD (Clegg et al., Arthritis Rheum 39: 2013-20, 1996). Some studies have indicated that the immunosuppressor cyclosporine is effective in treating PsA (reviewed in Salvarini et al., 1998), though this drug has severe side effects. In addition, others have proposed that PsA could be treated with truncated TNFα receptors or with a combination of methotrexate and antibodies against TNFα (WO 98/01555; WO 98/0537).
A recent meta-analysis of a number of PsA treatment studies concluded that PsA and RA differed not only in their response to treatment with specific drugs, but in the relative magnitudes of improvement in the placebo arms of the studies (Jones et al., Br J Rheumatol 36:95-99, 1997). As an example, PsA patients responded better to gold salt therapy than did RA patients, though the gold did not affect the psoriatic skin lesions (Dorwart et al., Arthritis Rheum 21:515-513, 1978).
It has been suggested that the suppression of TNFα might be beneficial in patients suffering from various disorders characterized by abnormal or excessive TNFα expression. However, although progress has been made in devising effective treatment for such diseases, improved medicaments and methods of treatment are needed.